The present invention relates to a charged particle beam apparatus, and more particularly to a charge particle beam apparatus in which vibration or swinging becomes a problem such as a scanning electron microscope, a charged particle beam processing apparatus and the like.
In a charged particle beam apparatus, vibration propagating from a floor is commonly intercepted or suppressed by mounting the apparatus on a vibration isolating table. As the vibration isolating table also used is an active vibration isolating table which actively varies position and height of the table in order to suppress vibration.
For coping with image troubles or processing troubles due to vibration of a sample stage, there is a method in which vibration in a the sample stage or a column is measured using a vibration pickup or the like and an operator is waiting until the vibration disappears (Japanese Patent Application Laid-Open No.64-69011), and a method in which a vibration signal of a sample stage is processed and the processed signal is added to a deflecting signal of a deflector (scanning signal) (Japanese Patent Application Laid-Open No.61-23317). In regard to methods of preventing vibration of a column or a sample stage, methods are proposed in Japanese Patent Application Laid-Open No.1-227436, Japanese Patent Application Laid-Open No.5-47645 and Japanese Utility Model Laid-Open No.1-87533.
In a scanning electron microscope and the like, as the resolution is being improved, the vibration cannot be eliminated sufficiently by a commonly used vibration isolating table. Accordingly, an active vibration isolating table is partially used. However, the active vibration isolating table cannot sufficiently remove vibration or rolling of such a very low frequency as approximately 1 Hz, which becomes an obstacle to improve the resolution in the environment where the scanning electron microscope is actually used. Further, even if vibration from the floor can be reduced by using the vibration isolating table, there are some cases where the structure on the vibration isolating table resonates with sound vibration to cause very small vibration which degrades an image of the scanning electron microscope or the like.
That is, it is revealed that rigidity of the mechanical structure of the conventional scanning electron microscope is too low to attain a required resolution. Particularly, in a case where size of the sample chamber is increased in order to observe a large sized sample such as a semiconductor wafer having a large diameter in recent years, rigidity of the sample chamber is reduced to cause rolling easily. It is clarified that this is main cause to produce an image deformation by vibration. Further, it is also clarified that electromagnetic wave existing inside the sample chamber deflects the electron beam, which may cause image trouble. However, sufficiently high rigidity of the apparatus may result in an unrealistic solution that wall thickness of the members must be increased by digits.
On the other hand, trouble due to vibration is determined by positional relationship between the column having an optical system of charged particle beam and the sample stage holding a sample, and accordingly change in relative positional relationship between the column and the sample stage, that is, a relative vibration signal cannot be obtained if vibration of only the sample stage or only the column is measured. Therefore, it is incomplete also from the theoretical view point that the trouble of vibration and rolling is removed by the common methods.
Furthermore, when the charged particle optical system is set to high resolution type, a low-magnified and wide-view-field image is likely to be deformed in its periphery. In the conventional apparatus, no measures for such a problem are taken.